ドワーフ竹は、ドングリを食べるネズミにも生息地を提供することで、動物園樹の再生に大きな影響を与えていることがわかりました

Dwarf bamboos affect the regeneration of zoochorous trees by providing habitats to acorn-feeding rodents.

• Naoya Wada

抄録

本研究では、アネモコール（Acer palmatum var. matsumurae, Fraxinus lanuginosa, Carpinus laxiflora）とズーチョア（Qercus mongolica var. grosseserrata, Q. serrata）の苗木と苗木の空間的分散を分析することにより、天然広葉樹林における矮性竹（Sasa spp.また、地上10cmにおける相対的な光合成光束密度は、矮性竹の被覆率と有意な相関があった（r=0.661、P<0.001）。また、日陰耐性のイソギンチャクA. palmatum var. matsumuraeとF. lanuginosaでは苗木の分布は不規則であったが、日陰耐性のイソギンチャクC. laxifloraではササがまばらな場所に集合していた。また、日陰耐性種のQ. serrataと耐性種のQ. mongolica var. grosseserrataでは、苗木が集合し、ササの被覆量と負の相関があった。また、ササが密生している場所では、林床に置かれたドングリは、Apodemus speciosusやA. argenteusのような小型のげっ歯類によって速やかに除去された。齧歯類のトラップセンサスの結果、これらの哺乳類はまばらなササの生息地よりも密なササの生息地を好むことが明らかになった。このことから、ドワーフバンボは苗木を遮光するだけでなく、ドングリを食べる小動物にも生息地を提供することで、動物園樹の再生に強い影響を与えていると考えられます。

The effects of dwarf bamboos (Sasa spp.) on the regeneration of trees in a natural hardwood forest were studied by analysing the spatial dispersion of seedlings and saplings of anemochores (Acer palmatum var. matsumurae, Fraxinus lanuginosa, and Carpinus laxiflora) and zoochores (Quercus mongolica var. grosseserrata and Q. serrata). Relative photosynthetic photon flux density at 10 cm above ground was significantly correlated with the coverage of dwarf bamboos (r=0.661, P<0.001). Seedlings were abundant and were randomly distributed in the anemochores, other than the shade-intolerant species C. laxiflora which was significantly more sparse in sites with dense Sasa than in sites where Sasa was rare. Distribution of saplings was also random in the shadetolerant anemochores A. palmatum var. matsumurae and F. lanuginosa but aggregated in sites with sparse Sasa in the shade-intolerant anemochore C. laxiflora. In contrast to the anemochores, seedlings of zoochores were very few and were distributed in sites with sparse Sasa. Saplings were also aggregated and negatively correlated with Sasa cover in the shade-intolerant species Q. serrata and the tolerant species Q. mongolica var. grosseserrata. The acorns put on the forest floor in a site with dense Sasa were quickly removed by small rodents such as Apodemus speciosus and A. argenteus. Trap census of rodents revealed that those mammals prefer the dense Sasa habitat to the sparse Sasa habitat. This suggests that the dwarf bamboos strongly affect the regeneration of zoochorous trees not only by shading the seedlings but also by providing habitats to acorn-feeding small mammals.